Re: [ATM] diagonal flat testing

[Mark Suchting <masuch@cia.com.au>]

A nice exposition here of the quantitative Ritchey - Common flat test  :

http://astro.umsystem.edu/atm/ARCHIVES/FEB01/msg00617.html

~Mark



At 10:41 PM 4/29/2004 -0700, Dale Eason wrote:


>A friend just showed me a similar test but the
>diagonal is placed very close to the mirror.  Place
>both mirrors at the test stand location.  Rotate the
>spherical mirror away from the tester so that it faces
>the diagonal which is at 45 deg to the spherical and
>the tester.  Imagine it as a very short newtonian with
>a very long eyepiece.  The distance from diagonal to
>tester should be about the ROC minus the distance from
>mirror to diag.  Use the ronchi at 45 deg from
>vertical.  As you shift the ronchi from inside to
>outside COC the image of the lines should not rotate.
>If they do the diagonal is not perfect and has some
>astig.
>
>I tried it with one bad and one good diagonal. It
>works.
>
>Dale Eason
>--- "Jerry B. Hillman" <JBHillman@ev1.net> wrote:
> > Hi All,
> > At the suggestion of Ken Hunter, I set up my
> > Foucault Tester with the
> > spherical 5" primary from my Meade scope.  After
> > getting everything aligned
> > I did the Foucault null test for a sphere and also a
> > Ronchi test.  As
> > expected, both tests showed a decent spherical
> > surface.
> > Then I added the diagonal flat into the light path
> > about 12" away from the
> > light source.  Of course this required turning the
> > tester at right angles to
> > the mirror, and angling tester and both mirrors to
> > get everything back into
> > alignment so I could see the reflected light.  Now
> > the light is passing
> > across the diagonal flat twice.  Once on the way to
> > the mirror and again on
> > the return path.This wasn't an easy task to get set
> > up.
> > Results however seem to confirm that the diagonal
> > flat is indeed polished
> > flat.  At least I still get the same results when
> > doing the null test and
> > the Ronchi test.  I would assume that if the
> > diagonal was not correct I
> > would be able to detect problems in one of these
> > tests.  Incomplete nulling
> > of the sphere or crooked or twisted Ronchi lines.
> > By the way, the Ronchi
> > lines were straight, edge to edge, both sides of
> > focus with as many or as
> > few lines as I cared to display.
> > I would like to be told if my testing method was
> > invalid or incorrectly
> > done, as I have never attempted this type of test
> > before and I intend to get
> > this flat and the 16.5" coated next week provided
> > that the 16.5" passes the
> > set of Foucault tests I am about to run on it.
> > I'll check my e-mail again before I send these
> > mirrors off Saturday just in
> > case.
> > Clear skies, Jerry
> >
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
>
>
>
>
>
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